Ultra-violet radiation absorbing silicon particle nanoclusters

ABSTRACT

Silicon particle nano-clusters formed with crystalline cores and amorphous shells are used for absorbing ultraviolet wavelength radiation. Silicon nano-particles are synthesized by plasma-chemical sputtering of bulk silicon crystal to form particles which are then quenched in an atmosphere of oxygen or oxygen and nitrogen. Analysis of these particles is presented for their scattering and absorption properties for use as ultraviolet protection elements.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and is a continuation-in-part ofU.S. provisional application Ser. No. 60/730,271 filed on Oct. 26, 2005;and is a continuation-in-part of U.S. application Ser. No. 11/094,837filed on Mar. 30, 2005, which is a continuation-in-part of U.S.provisional application Ser. No. 60/558,209 filed on Mar. 30, 2004. Eachof these applications is hereby expressly incorporated by reference intheir entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

REFERENCE TO A MICROFICHE APPENDIX

Not Applicable.

RESERVATION OF RIGHTS

A portion of the disclosure of this patent document contains materialwhich is subject to intellectual property rights such as but not limitedto copyright, trademark, and/or trade dress protection. The owner has noobjection to the facsimile reproduction by anyone of the patent documentor the patent disclosure as it appears in the Patent and TrademarkOffice patent files or records but otherwise reserves all rightswhatsoever.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to improvements in radiation protection.More particularly, the invention relates to the use of silicon particlenano-clusters formed with crystalline cores and amorphous shells thatare used for absorbing ultraviolet wavelength radiation in a protectionscheme.

2. Description of the Known Art

As will be appreciated by those skilled in the art, siliconnanoparticles are known in various forms. Patents disclosing informationrelevant to silicon nanoparticles include U.S. Pat. No. 7,078,276,issued to Zurcher, et al. on Jul. 18, 2006; U.S. Pat. No. 7,020,372,issued to Lee, et al. on Mar. 28, 2006; U.S. Pat. No. 7,005,669, issuedto Lee on Feb. 28, 2006; U.S. Pat. No. 6,961,499, issued to Lee, et al.on Nov. 1, 2005; U.S. Pat. No. 6,846,565, issued to Korgel, et al. onJan. 25, 2005; and U.S. Pat. No. 6,268,041, issued to Goldstein on Jul.31, 2001; U.S. Pat. No. 6,992,298, issued to Nayfeh, et al. on Jan. 31,2006.

Other publications to consider include:

-   1. Canham, L. T., Appl. Phys. Lett., 1.990, vol. 57, p. 1046;-   2. Klein, K., Sun Products: Protection and Fanning. Carol Stream;    Allured, 1998, p. 5;-   3. Ishchenko, A. A., Storozhenko, P A., Tutorskii, I A., et al, RF    Patent 2 227 015, 2003;-   4. Zhu, Y, Wang, H., and Ong, P R, Appl. Surf Sci., 2001, vol.    171, p. 44;-   5. Roldughin, V I., Usp. Khim., 2003, vol. 72, p. 931;-   6. Huang, F.-C., Lee, J.-F, Lee, C. K., and Chao, H. P., Colloids    Surf., A, 2004, vol. 239, p. 41;-   7. Delerue C., Allan 0., Lannu M.//J. Lumin. 1990. V. 80. P. 65-73;-   8. Soni R. K., Fonseca L. F., Resto 0., Buzaianu M., Weisz S. Z.    II J. Lumin. B. 1999, V. 83-84. P. 187-191;-   9. Altman I. S., Lee D., Chung J. D., Song J., Choi M. II Phys.    Rev. B. 2001. V. 63. P. 161406-   10. Knief S., WolfganvonNiessen.//Phys. Rev. B. 1999. V. 59. P.    12940-12945-   11. Tsutomu Shimizu-Iwayama, Takayuki 1-lama, David F. Hole, Ian W.    Boyd.//Solid-State Electronics. B. 2001. V. 45. P. 1487-1494-   12. Kuzlmin G. P., Karasev M. E., Khokhlov E M., Kononov N. N.,    Korovin S. B., Plotnichenko V. G., Polyakov S N., Pustovoy V I. and    Tikhonevich 0.V.//Laser Physiks 2000. V. 10. P. 939-945-   13. Beckman D., Beiogorokhov Al., Guseinov Sh. L. Ischenko A. A.,    Storojenko P. A., Tutorskyi l. A.,//Patent RU No. 2227015 Under the    application for the invention from 05.06.2003 r.-   14. Popov A. P., Kirillin M. Yu., Priezzhev A. V., Lademann J.,    Hast J. a. Myllyla P. Proc. SPIE,//Optical Diagnostics and Sensing    V, B. 2005. V. 5702. P. 113-122.-   15. Marchenko V. M., Koltashev V. V., Lavrishev S. V., Murin D. I.,    Plotnichenko V. 0.//Laser Physics. B. 2000. V. 11. P. 340-347-   16. Matsumoto T., Belogorokhov A. I. Belogorokhova L I., Masumoto    ‘1.//Nanoteclmology. B. 2000 V. 11. P. 340-347.-   17. Belogorokhov A I., Bublik V T., Scerbachev K. D., Parhomenko Yu.    N, Makarov V. V., Danilin A. V.//Nucl. Instruments and Methods in    Phys. Res. B. 1999, V. 147, P. 320-326-   18. Sahu B. S., Agnihotri O P., Jam S. C., Mertens R. a. Kato    I.//Appl. Opt. I B. 1990. V. 29. P. 3189-3496.-   19. Abdyurkhanov l. M., A˜wopxauoB K M., Prusakov B. F., Gorelik V    S., Plotnichenko B. G.//Physical metallurgy and heat treatment of    metals. 1998. No. 10. C.15-17; and-   20. “Handbook of optical Constants of Solids”, Ed. by Edward D.    Palik, Aead. Press. San Diego 1998, P. 1, P. 11, P. 561-565, P.    575-579.

Each of these patents and/or publications is hereby expresslyincorporated by reference in their entirety. As noted by thesedisclosures, the prior art is very limited in its teaching andutilization, and an improved nanocrystaline based ultraviolet radiationscreen is needed to overcome these limitations.

SUMMARY OF THE INVENTION

The present invention is directed to an improved radiation protectionscheme. In accordance with one exemplary embodiment of the presentinvention, nancrystalline silicon is shown to provide an effectiveultraviolet absorption barrier for protection from radiation.

The present invention is directed to the structure of the particles ofnanocrystalline silicon synthesized in argon plasma with added oxygen.An amorphous shell composed of silicon oxide is formed on the surface ofsilicon nanoparticles. The particles form clusters with a fractalstructure. The present invention discusses the adsorption of nitrogen ona powder of nanocrystalline silicon at 77 K, and adsorption isothermsobtained for nanocrystalline silicon and nonporous silica adsorbentswith identical specific surface areas are compared. The values ofsurface fractal dimension of powdered nanocrystalline silicon arecalculated using the Frenkel-Halsey-Hill equation for multilayeradsorption under the dominant contribution of van der Waals or capillaryforces. It is shown that surface fractal dimension is astructure-sensitive parameter characterizing both the morphology ofclusters and the structure (roughness) of the surface of particles andtheir aggregates.

In addition, the present invention discloses the optical properties ofan emulsion of nanocomposite materials based on silicon powder. Alsoprovided is the method of creation of a new type of emulsion composite,allowing the control of the spectral structure of transmittedelectromagnetic radiation. Two embodiments of silicon powder material,containing SiOx (type 1) and SiOx+SiNx (type 2) depending on conditions,are shown to provide varying effects. The results of FTIR-spectroscopyof powder silicon show the formation of SiO2 and SiOx phases on thesurface layer of sample type 1 and the formation of nitride phase on thesurface layer of sample type 2. The Raman Spectroscopy investigation oftwo series of samples provides the determination of the dimensions ofnanoparticles and their phase structure in the silicon powders. TheRamen Spectra of samples type 1 and type 2 within the range of 500-600CM1 demonstrates that the silicon powder is nanocrystalline silicon withdimension of d=10±2 nm for type 1 and d=13±2 nm for type 2. Emulsioncomposite samples with nanocrystalline silicon are provided and a testrun of these materials was performed. The Spectra of optical density aswell as the spectra of transmission and diffusive reflection intointegrative spheres were measured for both types of samples. It wasshown that the samples of type 2 are preferable as the most effectiveprotective ingredients of sunscreens.

These and other objects and advantages of the present invention, alongwith features of novelty appurtenant thereto, will appear or becomeapparent by reviewing the following detailed description of theinvention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the following drawings, which form a part of the specification andwhich are to be construed in conjunction therewith, and in which likereference numerals have been employed throughout wherever possible toindicate like parts in the various views:

FIG. 1 is an X-ray diffraction pattern of four samples of nanocrystalinesilicon with asterisks denoting peaks referred to A1.

FIG. 2 is an X-ray diffraction pattern of nanocrystaline siliconprepared with atmospheric oxygen.

FIG. 3 is electron photomicrographs of samples (a,b) 1 and (c,d) 2 ofnanocrystaline silicon with (c) showing initial observation and (d)showing the after effect of seven minutes of electron beam.

FIG. 4 shows adsorption isotherms of nitrogen at 77.3 k obtained forthree different samples of nanocrystaline silicon.

FIG. 5 shows adsorption isotherms of nitrogen at 77.3 k obtained for (1)Aerosil AS-2 and (2) nanocrystaline silicon with specific surface areasof 55 m²/g.

FIG. 6 shows a comparison of adsorption values at identical relativepressures obtained for standard Aerosil AS-2 and NS with specificsurface areas of 55 m²/g with adsorption on NS plotted on the abscissaaxis and adsorption on standard Aerosil on the ordinate axis.

FIG. 7 shows the determination of surface fractal dimensions for threesamples of nanocrystaline silicon.

FIG. 8 shows pictures of silicon nanoparticles of type I atmagnification.

FIG. 9 shows the infrared spectra of samples types I and II.

FIG. 10 shows the Raman spectrum of silicon powder incorporated into thematrix of silicate glue (1-2%) as well as the Raman spectrum ofcrystalline silicon.

FIG. 11 shows the transmission spectrum T(λ) of emulsions containingnanocrystaline silicon of type I, optical density changing (a)

transmission spectrum into sphere (b) and presenting at the insert thetransmission spectrum of the initial sample containing 1% powder Si (1)and after heat treatment at 800° (2).

FIG. 12 shows the transmission spectrum T(λ) of emulsions containingnanocrystaline silicon of type II, optical density changing (a)

transmission spectrum into sphere (b).

FIG. 13 shows diffuse reflection (squares) and transmission (dots) of Sinanoparticle dredge (including volume fraction 0.5%) within a 20-mkmlayer of water-oil media (for incident raditation with wavelength 290(a), 350 (b)

400 Hm (c)) in dependence of average Si nanoparticle diameter (d) fordifferent wavelength of incident radiation at particle diameter of 10nm.

DETAILED DESCRIPTION OF THE INVENTION

First, we take a look at the structure and adsorption properties ofnanocrystaline silicon. In recent years, ever increasing interest iscaused by nanostructured systems. Nontrivial properties of these systemsmake it possible to find their unexpected application in diverse objectsincluding the development of new functional elements and composites. Theunique properties of nanosized objects are determined mainly by theeffect of the surface on atomic and electronic processes at a quantumlevel. The bulk part of nanocrystals is formed by the initial crystallattice whose average size is of several tens of nanometers. This sizepredetermines the region of the localization of wave functions ofelectrons and holes. For this reason, optical and electron properties ofnanocrystals where the motion of charge carriers is limited in two(quantum lines) or three (quantum dots) directions are different thanthose of their bulk analogs. Among the objects with altered opticalproperties, the nanocrystalline silicon (NS) is the most attractivesubstance due to its ability to shift the edge of major absorption tovisible and ultraviolet regions.

At present, there are two main classes of complex emulsion media, whichare used for the absorption of ultraviolet radiation. In the firstclass, chemical compounds with chromophore groups absorbing radiation inthe UV region are used. In the second class of compounds, strongscattering of photons from the ultradispersed particles of some metaloxides incorporated into the matrix is employed. However, practicalapplication of these media can lead to negative consequences. Forexample, as was shown in some works, their application as sunblockingmaterials gives rise to the emergence of melanoma due to the TJVdegradation of proteins and the formation of active radicals.

For the development of sunblocking composites, others have proposed touse the physical effect of the UV photon absorption without thereemission of photons with different energy characteristics. Theseproposal have been limited in their success. However, this effect can berather simply implemented in the NS particles, because variations intheir sizes and surface modification allow us to control their opticalproperties. In turn, knowledge of the interrelation between thestructure of nanosized particles and their optical properties makes itpossible to purposefully develop new production technologies ofsunblocking composites.

The powdered NS was synthesized in argon plasma in a closed gas cycle.Deep gas cleaning from moisture and oxygen impurities was performedusing aluminum melt or special finishing cleaning agents that reversiblyabsorb impurities up to several parts per billion. The system was filledwith argon from the main line. The gas was circulated using a membranepump. Compressed gas was fed trough the receiver to rotameter ramp andthen was redistributed to the blocks of plasma unit. A plasmaevaporator-condenser operating in a low-frequency arc discharge was useda reactor. The initial raw material was silicon powder, which wassupplied to the reactor by the gas flow from the dosing tank. The powderin the reactor evaporated at 7000-10000° C.

At the outflow from the high-temperature plasma zone, the obtainedgas-vapor mixture was subjected to abrupt cooling with the gas jetsresulted in the condensation of silicon vapor and formation of anaerosol. The obtained aerosol with temperature of 100-200° C. was fed tothe refrigerator where it was cooled to 60-80° C. Large particles,together with unreacted fraction including unprocessed fraction, wereseparated from the ultradispersed powder in an inertial classifier.

The resultant powder was then collected on a hose-type cloth filter.From the filter, the powder was discharged in an inert atmosphere in abox into a hermetic vessel or was transported to a microencapsulationsystem where the inert protective layer preventing the powder fromambient effects was deposited onto the powder surface,

Photomicrographs were taken with a Fillips EM-301-NED transmissionelectron microscope at an accelerating voltage of 80 kV. The NS powderwas deposited onto a copper grid placed on a carbon substrate.

The X-ray diffraction analysis was performed with a Shimadzu LabXRD-6000 instrument with CuK_(α) radiation with Ni filter at a currentof 20 mA, a voltage of 40 kV, and a scanning rate of 4 deg/min. Equalamounts (about 1.00 mg) of NS powder on the aluminum substrate wasplaced in a cell and X-ray diffraction patterns were obtained at 20angles varying from 20° to 120°.

Isotherms of low-temperature nitrogen adsorption at 77.3 K were measuredon a Gravimat-4303 automatic vacuum adsorption unit with a sensitivityof I jig for a sample of 100 mg at a relative pressure varied from 104to 0.9.

Four NS samples prepared in the induction argon plasma under differentconditions were studied. The results of the initial four samples aredetailed in the figures and the following detailed discussion.

FIG. 1 shows X-ray diffraction patterns for four NS samples. The degreeof crystallinity was calculated by the integral intensity of the mostcharacteristic peak at 2θ=28° assigned to nanocrystalline silicon.

The diffraction pattern of the first sample prepared under theconditions that allow for the contact between the aerosol and air ispresented in FIG. 2. The presence of diffuse scattering halo in therange of 2θ=20°-30° corresponding to amorphous SiO₂ indicates thesurface oxidation of silicon particles and the formation of particleswith the structure of “core-shell” type where the core is the siliconnanocrystal and the shell consists of silicon oxide of various degreesof oxidation. According to this data, the degree of sample crystallinityis ˜10%. Relative intensity of the peaks at 2θ=20°-30° corresponding tocrystalline silicon for samples 1-4 is arranged in the series 1.0, 3.6,3.4, and 4.2. Consequently, the degree of crystallinity for the studiedsamples was 10, 36, 34, and 42%, respectively. As is seen from FIG. 1,the background on the X-ray pattern becomes less intense with anincrease in the degree of crystallinity that corresponds to a decreasein the fraction of amorphous phase.

The degree of crystallinity of NS particles characterizes the ratio ofthe number of atoms forming the crystal core to the number of atomsforming the amorphous shell. These data do not allow us to estimate theshell thickness and the degree of core coverage, i.e., the continuity ormosaicity of a shell. It is also impossible to determine the proportionbetween silicon with different degrees of oxidation.

The morphology of NS powder was studied by transmission electronmicroscopy. FIG. 3 demonstrates the photomicrographs of various NSsamples. On photomicrographs, one can distinguish between the branchedaggregates (clusters) formed by the particles with sizes of 20-30 nm.The shape of aggregates changed during the observation, thus indicatingthe aggregate disintegration under the action of electron beam. Localdestruction of small aggregates and thinning of chains formed bynanoparticles can be seen in photomicrographs (FIGS. 3 c and 3 d). Thedisintegration of aggregates occurs due to the entrainment of siliconatoms or nanoparticles with sizes smaller than 10 nm.

Fractal dimension df of NS aggregates was determined from electronmicroscopy images using the box-counting method used in the art. Thevalues of fractal dimension were calculated from the aggregateprojections. TABLE 1 Magnification 1 × 10⁵ 5 × 10⁴ 3.3 × 10⁴ Sample 11.72 1.82 1.79 Sample 2 1.68 1.70 1.67

Table 1 shows fractal dimension d_(f) determined by the projection ofpowdered NS aggregates at different image magnifications. As is seenfrom Table 1, there is a satisfactory agreement between the d_(f) valuesobtained for the same sample at different magnifications. This isindicative of the hierarchic structure of NS aggregates preserving thefractal structure at various levels, i.e., of the presence ofself-similarity as one of the main features of fractal systems.

The coincidence of d_(f) values for different samples indicates theresemblance of their preparation conditions and the structure ofaggregates.

The structurization of powdered NS is determined by the surfaceproperties of a shell composed of silicon oxide with different degreesof oxidation. Surface properties were studied by the technique oflow-temperature nitrogen adsorption. This method also makes it possibleto draw some conclusion about the morphology of powders and the presenceof pores. We performed comparative study of low-temperature nitrogenadsorption on nanocrystalline silicon and different silica adsorbents(silica gels) with known specific surface area and surface structure.

FIG. 4 demonstrates the isotherms of low-temperature nitrogen adsorptionon various NS samples. The obtained isotherms belong to type II(according to Brunauer's classification) and are characterized by alarge slope in the saturation region with the predominant polymolecularadsorption.

Using obtained isotherms, we calculated the values of specific surfaceareas by the linearized BET equation and the characteristic energy ofadsorption by the Dubinin-Radushkevich equation.

We also compared nitrogen adsorption isotherms for nanocrystallinesilicon and nonporous silica adsorbents with similar values of specificsurface areas (determined by the BET technique).

FIG. 5 shows the adsorption isotherms for two adsorbents with similarvalues of specific surface areas: Aerosil with a specific surface areaof 55 m2/g (curve 1) and NS with the same value of specific surfacearea. We also compared the adsorption values at the same relativepressures for these two adsorbents (FIG. 6). The values of adsorption onNS are plotted on the x axis; those on standard Aerosil, on the y axisat the same relative pressures. The value of correlation coefficient(the reliability of linear approximation) appeared to be 0.99.

The coincidence of adsorption properties of NS with specific surfacearea of 110 m2/g and nonporous silica and silica gel with the samespecific surface areas is also quite satisfactory. This means thatnanocrystalline silicon is a nonporous adsorbent.

Thus, the specific surface area of adsorbent characterizes neither thesurface structure of NS primary particles nor the structure of itsaggregates. Therefore, the necessity arises to search for othercharacteristic of adsorbent which is a structure-sensitive parameter.

For this purpose, we calculated the values of surface fractal dimensionof powdered NS using the Frenkel-Halsey-Hill equation for polymolecularadsorption generalized to the case of fractal surfaces.

The equation has the following form:$\left. \frac{N}{N_{m}} \right.\sim\left\lbrack {{RT}\quad\ln\frac{P_{s}}{P}} \right\rbrack^{{- 1}/m}$

where N/Nm is the degree of surface coverage; P and Ps are theequilibrium pressure and the saturated pressure adsorbate vapor,respectively; and m is the slope of the straight line to the ordinateaxis.

The pattern of adsorption isotherm for fractal surfaces depends on theprevalence of the type of adsorption forces in the adsorption process.If van der Waals forces acting between the adsorbent and adsorptionlayer dominate, the value of fractal dimension D of the surface iscalculated by equation$D = {3\left\lbrack {1 - \frac{1}{m}} \right\rbrack}$

If the dominating forces are the capillary forces determined by thesurface tension at the gas-liquid interface, the D value is calculatedby equation $D = {3 - \frac{1}{m}}$ TABLE 2 Surface fractal dim.Calculated by Calculated by Sample S_(sp), m²/g Eq. 2 Eq. 3 1 55 1.712.57 2 110 1.95 2.65 3 60 1.85 2.62

Table 2 shows surface fractal dimensions of NS. TABLE 3 No. Preparationconditions and characteristics 1 2 3 4 1 Plasma-forming gas Ar Ar Ar +O₂ N₂ 2 Plasma temperatures, ° C. 1 × 10⁴ 1 × 10⁴ — 7.3 × 10³ 3 Meanparticle size, nm 18 11 — 20 4 Peak intensity on diffraction pattern 8092964 2749 3412 5 Degree of crystallinity 10 36 34 42 6 Specific surfacearea (by BET), m²/g 55 110 60 — 7 Activation energy of adsorption,kJ/mol 12.5 11.5 — — 8 Fractal dimension over the area, d_(f) 1.67 1.78— 9 Surface fractal dimension D at the prevalence of: van der Waalsforces 1.71 1.95 1.85 — capillary forces 2.57 2.65 2.62 —

Table 3 shows the structural and morphological parameters of powdered NSprepared under different conditions.

FIG. 7 illustrates experimental dependences in log-log coordinates;Table 2, the values of surface fractal dimension calculated by thelinear parts of these dependences and Eqs. (2) and (3). As is seen fromthese data, the values of surface fractal dimension calculated by therelation corresponding to the prevalence of capillary forces fitinterval 2-3.

The values of surface fractal dimension calculated by the relationcorresponding to the prevalence of van der Waals forces turned out to besmaller than two, i.e., lower than the value permissible for the roughsurfaces. Consequently, the adsorption of nitrogen at 77 K onnanocrystalline silicon within the range of relative pressures of0.1-0.8 is determined by the capillary forces.

The dependence of structural and morphological parameters of powdered NSon the conditions of powder preparation is shown in Table 3.

Thus, so far we have shown that the combination of X-ray diffractionanalysis, transmission electron microscopy, and low-temperature nitrogenadsorption made it possible to establish that, in argon or nitrogenplasma with added oxygen, ultradispersed silicon particles composed ofcrystalline core and amorphous shell are formed. These particles formfractal clusters whose surface fractal dimension is astructure-sensitive parameter. Surface fractal dimension is anadditional quantitative characteristic of various adsorbents and polymerfillers.

Additionally, we consider the unique spectral properties of ananocomposite material based on silicon

Silicon particle nanoclusters, incorporated into various transparentmedia, are a new object of interest for this physicochemical study. Forparticles smaller than 4 nm the effects of dimensional quantization areessential, and their use permits control of the luminescent propertiesand absorbance of materials in UV spectral region. Optical properties ofthe particles with size of more than ˜10 nm are determined mainly by theoptical properties of bulk silicon crystals. These characteristicsdepend on a number of factors such as presence of structure defects,additives, phase state and some other factors.

The plasma technology of silicon powder production in variousatmospheres permits verification of the chemical composition of thenanoparticle surface layer. Such ability is not available by ionimplantation or radiofrequency precipitation which are the methodsordinarily used for preparation of nanocrystalline silicon.

As far as known to us, detailed study of spectra of composite materials,based on nano sized silicon powder have not been performed beforealthough spectra of nanosized silicon powders, produced by laser-induceddecomposition of gasiform SiH4, has been presented.

The creation of new effective UV-radiation protectors, based on siliconnanoparticles is the primary stimulating interest of this application. Asignificant advantage of these new materials is their ecological purity.By the changing of nanoparticles size distribution, their concentrationsin the composite, and modification of the particle surface, it becomespossible to control spectral characteristics of the nanocompositematerial as a whole. For effective protection of human skin, sunscreeningredients must limit and/or prevent UV transmission within, the rangeof wavelength less then 400 nm, that define sunscreen properties ofcommercial creams.

The main goal of this work was the study of spectral properties ofoil-water media containing prepared composite silicon nanoparticles withvariations in both silicon particle concentration and methods of itsproduction.

Specially prepared highly transparent silicon composite nanoparticlescapable of controlling wavelength, transmittance in the range of 200-850nm, and emulsified as water/oil was used as the base material ofsamples. The silicon powder was synthesized in a plasmatron in whichhigh-frequency induction plasma interacted with the silicon crystallinesamples. Nanoparticle synthesis was performed in an atmosphere of inertgases (He or Ar) with controlled addition of oxygen at the cooling stageof nanoparticle production. The samples of type I were synthesized bythis method. The active component of composite is a nucleus of siliconnanocrystals, obtained in oxygen atmosphere. By varying oxygen pressure(rate of oxygen introduction) the surface layer composition andthickness could be changed. The samples of type II were synthesized byadding controlled N2 gas into the atmosphere of oxygen.

The composite emulsions, were prepared by mechanical mixing of theprepared silicon powder types (1 & 2) with oil-water base at a definitemass proportions.

Originally a series of various methods were performed to test siliconpowder properties. The method of electronic microscopy (devicePhilips-EM-300) was used for obtaining the visual imaging of siliconpowder particles.

The Fourier infrared spectra were registered using Spectrometer IFS-113v(Bruker) within the range of wave numbers 4000-400 cm−1 with spectralresolution not more then 0,5 cm−1. A thin (˜20 μm) layer of the emulsionwas located inside special cells between silicon windows.

The Raman spectra were measured using monochromator T-64000 (Yobin Yvon)with excited radiation from argon laser (?=514,5 nm). The CCD-matrix wasapplied when cooled to 1.40 K for detection of Raman radiation. The bulksilicon crystal was used as the standard. The effect of samples heatingunder impact of laser radiation, which can essentially change Ramanscattering spectrum image, was tested and found to be negligible underour experimental conditions. In the set of experiments the samples wereprepared by incorporating the silicon powder into silicate glue. Suchtechniques provided stable, easy and multiple spectra measurements ofthe same sample in different experiments.

Spectrophotometer “Specord-M40” (Carl Zeiss, Jena) was used to studyspectra of transmission in the 200-850 nm optical range. The spectrameasurements were carried out using two different methods. The first oneallowed measurement of probe light attenuation in collimated geometry,providing data of optical density. In the second method, the diffusetransmission of the probe light into the integrating sphere wasmeasured. This allowed taking into account the power of radiation thatpassed through the sample in all directions inside 2π solid angle.Specifically designed cells with UV quartz windows were used to keep thethickness of investigated emulsions in the range of 10-20 micron.

Next, we take a look at the electron microscopy and infraredspectroscopy of silicon powder. The pictures of silicon nanoparticles oftype I, are presented in FIG. 8 at magnification. One can see that thesilicon particles generated by plasmatron are complex fractal aggregateswith a characteristic size of a few hundred nanometers which consist ofa number of smaller particles of more than 10 nm size.

The infrared spectra of Type I sample revealed an intensive band ofabsorbance at wave numbers 461, 799, 978, 1072 and 1097 cm−1 (FIG. 9).The appearance of these bands indicates the formation of phases SiO2 orSiOX (x=1.5-2). We assumed these phases are formed on the particlesurfaces. The spectra of the particles of Type ii bands at 60, 82, 1190and 1360 cm−1 revealed additional bands indicating formation ofoxynitrogen groups SiXOYNZ. The relation between components of thisphase is strongly dependent on the conditions of synthesis.

FIG. 10 presents Raman spectrum of silicon powder incorporated into thematrix of silicate glue (1-2%) as well as Raman spectrum of crystallinesilicon. The influence of glue spectrum bands on the spectra of siliconpowder was verified as rather small near the 521 cm⁻¹ peak atappropriate concentrations of silicon powder. The spectral band ofsilicon crystal is shifted to low frequencies with respect tocorresponding bands of both powder samples (types I and II) on about1.5-2.5 cm−1. Besides, the width of silicon powder peak is about 25%more of that for crystal silicon which is about 4 cm−1. Similar resultswere also obtained for Raman spectrum of emulsion, containing siliconparticles.

The analysis of the Raman spectra shows, that the structure ofsynthesized silicon powders of types I and II is close to crystallinesilicon. In the alternative case of amorphous silicon the width of peakwould be a few times more and its maximum would be in the range of480-490 cm−1.

According to known art, the shift of the Raman bands of silicon powdersto low frequency with respect to the band of crystalline silicon isconnected with the quantum size effect when the size of siliconparticles is decreased to nanometer scale.

To evaluate the size of particle it is possible to use the equation,which relates the shift of Raman band and size of particle (equation 4):${\Delta\gamma} \cong \frac{S^{2}}{4\quad c^{2}\gamma_{0}L}$

where S is the speed of sound in the crystal, c is the speed of light inthe crystal, γ₀ is the wavenumber of Raman band maximum for macroscopiccrystal, L is the characteristic size of silicon particle. Using thisequation the characteristic sizes of silicon particles were estimated as˜10±2 nm for samples of type I and ˜15±2 nm for samples of type II.Note, that the electron microscopy investigations are in well agreementwith the data of particle size estimated by Raman spectra analysis. Inthe conclusion of this section should be pointed that presentedevaluations of sizes of nanocrystal particles are quite approximate,because the averaged values of the sound speed in crystal and refractionindex within the visible spectrum range were used. The accuracy of sizeestimation by equation 4 is also decreased if the size of particlesincreases.

Nevertheless the used approach is defensible. For example, similarestimations of thickness of thin crystalline silicon films wellcorrelated with appropriate measurements by absorbance spectra.

Transmission spectrum T(λ) of emulsions, containing nanocrystallinesilicon, are presented in FIG. 11. These spectra correspond to change ofoptical density. Each series of spectra was registered for definitesample type with corresponding mass concentrations of silicon powder. Toreveal the influence of silicon powder on the composite transmittance weused an oil-water emulsion with high transparency within the entirerange of spectrum used. The spectra series for given types of powderrevealed some similarities. Namely, the spectra for 0.25 and 0.5%concentrations of silicon powder in emulsion are strongly changingdependencies T(λ), whereas for concentrations of about 1% higher thetransmittance is just changed slightly. Maximum light transmittance ofan emulsion of 20-micron thickness at 850 nm wavelength is less then 1%for both types of sample. It is important to note that for lowconcentrations of silicon powder (≦0.5%) the transmittance for thesample of type I increased with the wavelength increase but not for thesample of type II.

Spectral measurements of transmittance were made with the same siliconpowder samples using integrating sphere. These measurements permit oneto obtain more information about characteristic changing of compositetransmission because of taking into account the diffuse scattering into2π angle. The experiment is of practical interest from the viewpoint ofcreation of UV light protectors. FIG. 4 shows a quite high transmissionsignal within whole spectral region, including UV-range 230-400 nm.

The transmission level weakly depends on the concentration ofnanocrystalline silicon powder. Maxima within the range of 230, 280, 400nm on the FIG. 4 b, are connected most likely with the absorbance bandsof pure base and bands, corresponding to oxide covering and “silicon”nucleus. By increasing the concentration from 0.1 to 2% transmission fortype II sample is decreased greatly and becomes lower 7% in the range of200-450 nm.

Comparing results, presented on the FIG. 4 and FIG. 5, one can conclude,that for nanocrystalline silicon particles of type I the relativecontribution of light scattering effects on total transmittance islarger than that for particles of type II, especially in the range of200-450 nm. Yet for samples of type I the contribution of lightabsorbance by particles is determinative in UV range. It can be seenespecially for large concentrations of particles in emulsion. Takinginto account that nanocrystalline particles for samples of both typeshave similar size of “silicon” nucleus, these differences intransmission spectra are obviously connected to the presence ofchemically different surfaces, and therefore with difference of theiroptical properties.

As known, silicon oxynitrides have too much radiation losses withinUV-range compared with silicon oxides. Therefore the effect of lightabsorption for particles of type II can be determinative in measuringtransmission spectra by the integrating sphere due to presence of“oxynitride” covering, assuming the cover is quite thick in comparisonwith diameter of the particle. But effects of light scattering could bedeterminative at spectral measuring due to “oxide” covering. Thefollowing fact for this can be evidence. The transmittance of emulsionin UV range with silicon powder thermally treated in air during 1 hourat 600-800° is increased (see insert on FIG. 11 b). Also the infraredand Raman spectra of those samples indicate the increase of thickness of“oxide” covering and evidently a relative decrease of thickness of the“silicon” nucleus.

In consideration of the mechanism of spectra formation it is necessaryto take into account that Fresnel reflection$R \approx \left( \frac{n - n_{0}}{n + n_{0}} \right)^{2}$

for “oxide” layer is less of that for “oxynitride” layer, becauserefraction coefficient n is changed from 1.46 (for SiO2) to 2.0 (forSixOyNz). This circumstance could be kept in mind for more detailedanalysis of total light losses using as absorption spectra and thespectra of reflection.

In the conclusion of this section consider theoretically the influenceof size and concentration of pure silicon nanoparticles on theintegrated transmittance and reflectance of the media containing themfor various wavelengths. The chosen model parameters are close to theconditions of our experiments: the silicon spherical particles areassumed to be uniformly distributed in nonabsorbing media layer of 20 nmthickness and volume concentration of particles about 0.5% (≈1% massconcentration). The size of particles varied from 10 to a few hundrednanometers. The real and complex parts of refractive index of crystalsilicon were taken for wavelengths 290, 350 and 400 nm from previousnumbers known I the art while media refractive index was taken n₀=1.4assuming it independent of wavelength. Reflected and transmitted photonswere counted into solid angle 2π of appropriate back and straighthemispheres. The Monte-Carlo method based on Mie theory of lightscattering was used for calculations. Numerical results of ourcalculations are presented on FIG. 13. It shows that for givenwavelength there exists characteristic dimension of particles providingsimultaneously as minimal transmittance and maximal reflectance.Evidently, such correlation is the result of energy balance.

When decreasing of light wavelength this size is shifted to smallervalues: 60-90 nm for λ=400 nm, 40-100 nm for λ=350 nm and 25-1.00 nm forλ=250 nm. Note that for particles of minimal size used in ourcalculations (10 nm) transmittance is decreased quite steeply if thewavelength decreased (see FIG. 13 d). Presented dependence appeared moreclose to the data of sample of type I as a whole.

Thus, the spectral properties of an emulsion containing siliconnanoparticles are shown to be effective UV protectors. Two types ofsilicon nanoparticles were synthesized by plasmachemical sputtering ofbulk silicon crystal with the quenching of generated particles inatmospheres of oxygen and nitrogen. The synthesized siliconnanoparticles were determined by Raman spectroscopy as crystalline withcharacteristic size of about 1.0-15 nm. This size is well correlatedwith the data obtained by electron microscopy. Infrared spectroscopy ofthe samples containing silicon nanoparticles revealed a number ofcharacteristic bands of silicon oxides SiOx (x=1.5-2) and oxynitrogengroups, which presumably formed an envelope of a few nanometer thicknessthat cover the silicon crystal nucleus. This envelope could essentiallyinfluence the scattering and absorption properties of nanoparticlesdepending on the particles type. Particularly, scattering is moreeffective for SiO_(x) coverings while absorption effect is moreessential for Si_(x)O_(y)N_(z) coverings.

Theoretical analysis of the integrated by 2π solid angle transmittanceand reflectance of the silicon nanoparticles as a function of their sizeshows that a minimum of transmittance and a maximum of reflectance arewell correlated depending on the particles size and wavelength.

For particles of about 10 nm diameter the transmittance is stronglydecreased with the wavelength decrease to UV spectral range.

From the foregoing, it will be seen that this invention well adapted toobtain all the ends and objects herein set forth, together with otheradvantages which are inherent to the structure. It will also beunderstood that certain features and subcombinations are of utility andmay be employed without reference to other features and subcombinations.This is contemplated by and is within the scope of the claims. Manypossible embodiments may be made of the invention without departing fromthe scope thereof. Therefore, it is to be understood that all matterherein set forth or shown in the accompanying drawings is to beinterpreted as illustrative and not in a limiting sense.

When interpreting the claims of this application, method claims may berecognized by the explicit use of the word ‘method’ in the preamble ofthe claims and the use of the ‘ing’ tense of the active word. Methodclaims should not be interpreted to have particular steps in aparticular order unless the claim element specifically refers to aprevious element, a previous action, or the result of a previous action.Apparatus claims may be recognized by the use of the word ‘apparatus’ inthe preamble of the claim and should not be interpreted to have ‘meansplus function language’ unless the word ‘means’ is specifically used inthe claim element. The words ‘defining,’ ‘having,’ or ‘including’ shouldbe interpreted as open ended claim language that allows additionalelements or structures. Finally, where the claims recite “a” or “afirst” element of the equivalent thereof, such claims should beunderstood to include incorporation of one or more such elements,neither requiring nor excluding two or more such elements.

1. The method of formation of an ultraviolet radiation protectiondevice, comprising: synthesizing silicon nanoparticles by plasmachemicalsputtering of bulk silicon crystal to generate particles and quenchingthe generated particles in an atmosphere of oxygen to from synthesizedcrystalline silicon nanoparticles having a characteristic size between1.0 nm and 15 nm; and developing a layer of protection by dispersing thesynthesized crystalline silicon nanoparticles using a carrier.
 2. Themethod of formation of an ultraviolet radiation protection device,comprising: synthesizing silicon nanoparticles by plasmachemicalsputtering of bulk silicon crystal to generate particles and quenchingthe generated particles in an atmosphere of nitrogen to from synthesizedcrystalline silicon nanoparticles having a characteristic size between1.0 nm and 15 nm; and developing a layer of protection by dispersing thesynthesized crystalline silicon nanoparticles using a carrier.
 3. Anultraviolet radiation protection apparatus, comprising: synthesizedsilicon nanoparticles having a characteristic size between 1.0 nm and 15nm formed to have a crystalline core and an amorphous shell; and acarrier for dispersing the synthesized crystalline siliconnanoparticles.
 4. The apparatus of claim 3, wherein the amorphous shellis formed from a stable compound of silicon and oxygen.
 5. The apparatusof claim 3, wherein the amorphous shell is formed from a stable compoundof silicon, oxygen, and nitrogen.